Before we embark5 upon doubtful matters, let us try to find some more or less fixed6 point from which to start. Although we are doubting the physical existence of the table, we are not doubting the existence of the sense-data which made us think there was a table; we are not doubting that, while we look, a certain colour and shape appear to us, and while we press, a certain sensation of hardness is experienced by us. All this, which is psychological, we are not calling in question. In fact, whatever else may be doubtful, some at least of our immediate7 experiences seem absolutely certain.
Descartes (1596-1650), the founder8 of modern philosophy, invented a method which may still be used with profit—the method of systematic9 doubt. He determined10 that he would believe nothing which he did not see quite clearly and distinctly to be true. Whatever he could bring himself to doubt, he would doubt, until he saw reason for not doubting it. By applying this method he gradually became convinced that the only existence of which he could be quite certain was his own. He imagined a deceitful demon11, who presented unreal things to his senses in a perpetual phantasmagoria; it might be very improbable that such a demon existed, but still it was possible, and therefore doubt concerning things perceived by the senses was possible.
But doubt concerning his own existence was not possible, for if he did not exist, no demon could deceive him. If he doubted, he must exist; if he had any experiences whatever, he must exist. Thus his own existence was an absolute certainty to him. 'I think, therefore I am,' he said (Cogito, ergo sum); and on the basis of this certainty he set to work to build up again the world of knowledge which his doubt had laid in ruins. By inventing the method of doubt, and by showing that subjective12 things are the most certain, Descartes performed a great service to philosophy, and one which makes him still useful to all students of the subject.
But some care is needed in using Descartes' argument. 'I think, therefore I am' says rather more than is strictly certain. It might seem as though we were quite sure of being the same person to-day as we were yesterday, and this is no doubt true in some sense. But the real Self is as hard to arrive at as the real table, and does not seem to have that absolute, convincing certainty that belongs to particular experiences. When I look at my table and see a certain brown colour, what is quite certain at once is not 'I am seeing a brown colour', but rather, 'a brown colour is being seen'. This of course involves something (or somebody) which (or who) sees the brown colour; but it does not of itself involve that more or less permanent person whom we call 'I'. So far as immediate certainty goes, it might be that the something which sees the brown colour is quite momentary13, and not the same as the something which has some different experience the next moment.
Thus it is our particular thoughts and feelings that have primitive14 certainty. And this applies to dreams and hallucinations as well as to normal perceptions: when we dream or see a ghost, we certainly do have the sensations we think we have, but for various reasons it is held that no physical object corresponds to these sensations. Thus the certainty of our knowledge of our own experiences does not have to be limited in any way to allow for exceptional cases. Here, therefore, we have, for what it is worth, a solid basis from which to begin our pursuit of knowledge.
The problem we have to consider is this: Granted that we are certain of our own sense-data, have we any reason for regarding them as signs of the existence of something else, which we can call the physical object? When we have enumerated15 all the sense-data which we should naturally regard as connected with the table, have we said all there is to say about the table, or is there still something else—something not a sense-datum, something which persists when we go out of the room? Common sense unhesitatingly answers that there is. What can be bought and sold and pushed about and have a cloth laid on it, and so on, cannot be a mere1 collection of sense-data. If the cloth completely hides the table, we shall derive3 no sense-data from the table, and therefore, if the table were merely sense-data, it would have ceased to exist, and the cloth would be suspended in empty air, resting, by a miracle, in the place where the table formerly16 was. This seems plainly absurd; but whoever wishes to become a philosopher must learn not to be frightened by absurdities17.
One great reason why it is felt that we must secure a physical object in addition to the sense-data, is that we want the same object for different people. When ten people are sitting round a dinner-table, it seems preposterous18 to maintain that they are not seeing the same tablecloth19, the same knives and forks and spoons and glasses. But the sense-data are private to each separate person; what is immediately present to the sight of one is not immediately present to the sight of another: they all see things from slightly different points of view, and therefore see them slightly differently. Thus, if there are to be public neutral objects, which can be in some sense known to many different people, there must be something over and above the private and particular sense-data which appear to various people. What reason, then, have we for believing that there are such public neutral objects?
The first answer that naturally occurs to one is that, although different people may see the table slightly differently, still they all see more or less similar things when they look at the table, and the variations in what they see follow the laws of perspective and reflection of light, so that it is easy to arrive at a permanent object underlying20 all the different people's sense-data. I bought my table from the former occupant of my room; I could not buy his sense-data, which died when he went away, but I could and did buy the confident expectation of more or less similar sense-data. Thus it is the fact that different people have similar sense-data, and that one person in a given place at different times has similar sense-data, which makes us suppose that over and above the sense-data there is a permanent public object which underlies21 or causes the sense-data of various people at various times.
Now in so far as the above considerations depend upon supposing that there are other people besides ourselves, they beg the very question at issue. Other people are represented to me by certain sense-data, such as the sight of them or the sound of their voices, and if I had no reason to believe that there were physical objects independent of my sense-data, I should have no reason to believe that other people exist except as part of my dream. Thus, when we are trying to show that there must be objects independent of our own sense-data, we cannot appeal to the testimony22 of other people, since this testimony itself consists of sense-data, and does not reveal other people's experiences unless our own sense-data are signs of things existing independently of us. We must therefore, if possible, find, in our own purely23 private experiences, characteristics which show, or tend to show, that there are in the world things other than ourselves and our private experiences.
In one sense it must be admitted that we can never prove the existence of things other than ourselves and our experiences. No logical absurdity24 results from the hypothesis that the world consists of myself and my thoughts and feelings and sensations, and that everything else is mere fancy. In dreams a very complicated world may seem to be present, and yet on waking we find it was a delusion25; that is to say, we find that the sense-data in the dream do not appear to have corresponded with such physical objects as we should naturally infer from our sense-data. (It is true that, when the physical world is assumed, it is possible to find physical causes for the sense-data in dreams: a door banging, for instance, may cause us to dream of a naval26 engagement. But although, in this case, there is a physical cause for the sense-data, there is not a physical object corresponding to the sense-data in the way in which an actual naval battle would correspond.) There is no logical impossibility in the supposition that the whole of life is a dream, in which we ourselves create all the objects that come before us. But although this is not logically impossible, there is no reason whatever to suppose that it is true; and it is, in fact, a less simple hypothesis, viewed as a means of accounting27 for the facts of our own life, than the common-sense hypothesis that there really are objects independent of us, whose action on us causes our sensations.
The way in which simplicity28 comes in from supposing that there really are physical objects is easily seen. If the cat appears at one moment in one part of the room, and at another in another part, it is natural to suppose that it has moved from the one to the other, passing over a series of intermediate positions. But if it is merely a set of sense-data, it cannot have ever been in any place where I did not see it; thus we shall have to suppose that it did not exist at all while I was not looking, but suddenly sprang into being in a new place. If the cat exists whether I see it or not, we can understand from our own experience how it gets hungry between one meal and the next; but if it does not exist when I am not seeing it, it seems odd that appetite should grow during non-existence as fast as during existence. And if the cat consists only of sense-data, it cannot be hungry, since no hunger but my own can be a sense-datum to me. Thus the behaviour of the sense-data which represent the cat to me, though it seems quite natural when regarded as an expression of hunger, becomes utterly29 inexplicable30 when regarded as mere movements and changes of patches of colour, which are as incapable31 of hunger as a triangle is of playing football.
But the difficulty in the case of the cat is nothing compared to the difficulty in the case of human beings. When human beings speak—that is, when we hear certain noises which we associate with ideas, and simultaneously32 see certain motions of lips and expressions of face—it is very difficult to suppose that what we hear is not the expression of a thought, as we know it would be if we emitted the same sounds. Of course similar things happen in dreams, where we are mistaken as to the existence of other people. But dreams are more or less suggested by what we call waking life, and are capable of being more or less accounted for on scientific principles if we assume that there really is a physical world. Thus every principle of simplicity urges us to adopt the natural view, that there really are objects other than ourselves and our sense-data which have an existence not dependent upon our perceiving them.
Of course it is not by argument that we originally come by our belief in an independent external world. We find this belief ready in ourselves as soon as we begin to reflect: it is what may be called an instinctive33 belief. We should never have been led to question this belief but for the fact that, at any rate in the case of sight, it seems as if the sense-datum itself were instinctively34 believed to be the independent object, whereas argument shows that the object cannot be identical with the sense-datum. This discovery, however—which is not at all paradoxical in the case of taste and smell and sound, and only slightly so in the case of touch—leaves undiminished our instinctive belief that there are objects corresponding to our sense-data. Since this belief does not lead to any difficulties, but on the contrary tends to simplify and systematize our account of our experiences, there seems no good reason for rejecting it. We may therefore admit—though with a slight doubt derived from dreams—that the external world does really exist, and is not wholly dependent for its existence upon our continuing to perceive it.
The argument which has led us to this conclusion is doubtless less strong than we could wish, but it is typical of many philosophical35 arguments, and it is therefore worth while to consider briefly36 its general character and validity. All knowledge, we find, must be built up upon our instinctive beliefs, and if these are rejected, nothing is left. But among our instinctive beliefs some are much stronger than others, while many have, by habit and association, become entangled37 with other beliefs, not really instinctive, but falsely supposed to be part of what is believed instinctively.
Philosophy should show us the hierarchy38 of our instinctive beliefs, beginning with those we hold most strongly, and presenting each as much isolated39 and as free from irrelevant40 additions as possible. It should take care to show that, in the form in which they are finally set forth41, our instinctive beliefs do not clash, but form a harmonious42 system. There can never be any reason for rejecting one instinctive belief except that it clashes with others; thus, if they are found to harmonize, the whole system becomes worthy43 of acceptance.
It is of course possible that all or any of our beliefs may be mistaken, and therefore all ought to be held with at least some slight element of doubt. But we cannot have reason to reject a belief except on the ground of some other belief. Hence, by organizing our instinctive beliefs and their consequences, by considering which among them is most possible, if necessary, to modify or abandon, we can arrive, on the basis of accepting as our sole data what we instinctively believe, at an orderly systematic organization of our knowledge, in which, though the possibility of error remains44, its likelihood is diminished by the interrelation of the parts and by the critical scrutiny45 which has preceded acquiescence46.
This function, at least, philosophy can perform. Most philosophers, rightly or wrongly, believe that philosophy can do much more than this—that it can give us knowledge, not otherwise attainable47, concerning the universe as a whole, and concerning the nature of ultimate reality. Whether this be the case or not, the more modest function we have spoken of can certainly be performed by philosophy, and certainly suffices, for those who have once begun to doubt the adequacy of common sense, to justify48 the arduous49 and difficult labours that philosophical problems involve.
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1
mere
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| adj.纯粹的；仅仅，只不过 | |
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derived
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| vi.起源；由来；衍生；导出v.得到( derive的过去式和过去分词 )；（从…中）得到获得；源于；（从…中）提取 | |
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derive
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| v.取得；导出；引申；来自；源自；出自 | |
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strictly
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| adv.严厉地，严格地；严密地 | |
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embark
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| vi.乘船，着手，从事，上飞机 | |
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fixed
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| adj.固定的，不变的，准备好的；(计算机)固定的 | |
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7
immediate
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| adj.立即的；直接的，最接近的；紧靠的 | |
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Founder
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| n.创始者，缔造者 | |
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systematic
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| adj.有系统的，有计划的，有方法的 | |
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determined
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| adj.坚定的；有决心的 | |
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demon
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| n.魔鬼，恶魔 | |
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subjective
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| a.主观(上)的，个人的 | |
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momentary
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| adj.片刻的，瞬息的；短暂的 | |
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primitive
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| adj.原始的；简单的；n.原(始)人，原始事物 | |
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enumerated
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| v.列举，枚举，数( enumerate的过去式和过去分词 ) | |
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formerly
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| adv.从前，以前 | |
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absurdities
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| n.极端无理性( absurdity的名词复数 )；荒谬；谬论；荒谬的行为 | |
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preposterous
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| adj.荒谬的，可笑的 | |
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tablecloth
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| n.桌布，台布 | |
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underlying
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| adj.在下面的，含蓄的，潜在的 | |
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underlies
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| v.位于或存在于（某物）之下( underlie的第三人称单数 )；构成…的基础（或起因），引起 | |
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testimony
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| n.证词；见证，证明 | |
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purely
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| adv.纯粹地，完全地 | |
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absurdity
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| n.荒谬，愚蠢；谬论 | |
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delusion
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| n.谬见，欺骗，幻觉，迷惑 | |
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naval
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| adj.海军的，军舰的，船的 | |
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accounting
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| n.会计，会计学，借贷对照表 | |
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simplicity
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| n.简单，简易；朴素；直率，单纯 | |
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utterly
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| adv.完全地，绝对地 | |
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inexplicable
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| adj.无法解释的，难理解的 | |
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incapable
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| adj.无能力的，不能做某事的 | |
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simultaneously
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| adv.同时发生地，同时进行地 | |
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instinctive
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| adj.(出于)本能的；直觉的；(出于)天性的 | |
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instinctively
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| adv.本能地 | |
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philosophical
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| adj.哲学家的，哲学上的，达观的 | |
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briefly
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| adv.简单地，简短地 | |
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entangled
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| adj.卷入的；陷入的；被缠住的；缠在一起的v.使某人（某物/自己）缠绕，纠缠于（某物中），使某人（自己）陷入（困难或复杂的环境中）( entangle的过去式和过去分词 ) | |
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hierarchy
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| n.等级制度；统治集团，领导层 | |
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isolated
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| adj.与世隔绝的 | |
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irrelevant
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| adj.不恰当的，无关系的，不相干的 | |
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forth
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| adv.向前；向外，往外 | |
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harmonious
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| adj.和睦的，调和的，和谐的，协调的 | |
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worthy
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| adj.(of)值得的，配得上的；有价值的 | |
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44
remains
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| n.剩余物，残留物；遗体，遗迹 | |
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45
scrutiny
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| n.详细检查，仔细观察 | |
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46
acquiescence
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| n.默许；顺从 | |
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47
attainable
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| a.可达到的，可获得的 | |
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48
justify
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| vt.证明…正当(或有理)，为…辩护 | |
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49
arduous
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| adj.艰苦的，费力的，陡峭的 | |
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